To meet the market demand for a light, thin, and multi-functional electronic information product, techniques such as high-density interconnect (HDI) and high-layer count (HLC) have gradually been developed in the electronic packaging techniques of a printed circuit board (PCB), such that the electronic circuit density distributed inside the PCB is higher, but the volume is smaller, thus meeting the demand for a lighter and thinner device. A smaller PCB can result in more structural space in the end product design, and more functional components can be added to achieve the design concept of multiple functions on one device.
In particular, the definition of HDI includes a circuit board for which the thickness of a copper metal conductive layer is ≦25 μm, the thickness of an insulating layer is <75 μm, a linewidth of ≦20 μm, a line spacing of ≦20 μm, and an aperture of ≦100 μm. However, the current manufacturing method of an electronic circuit includes foil ling a copper foil layer by combining sputtering and a method of electroplating or a method of lamination of copper foil on a substrate, and then forming a circuit layer via a method of patterning. Then, the above steps of circuit layer manufacture are repeated to complete a high-density multilayer circuit board.
Electrical connection between the multilayer circuit boards is achieved via vias, and the manufacturing method of the vias can be conceptually divided into the electroplating method and the lamination method. The former includes complicated via process and has higher costs; and the latter cannot achieve thinning and miniaturization since the resulting circuit layer has thicker size and greater linewidth.